As illustrated in FIG. 15, a steering apparatus for an automobile is constructed so that rotation of the steering wheel 1 is transmitted to an input shaft 3 of a steering gear unit 2, and as the input shaft 3 rotates, that rotation pushes or pulls a pair of left and right tie rods 4, which apply a steering angle to the front wheels, which are the steered wheels. More specifically, the steering wheel 1 is supported by and fastened to the rear end section of a steering shaft 5, and the steering shaft 5, being inserted in the axial direction through the steering column 6, is supported by the steering column 6 so as to be able to rotate freely. Moreover, the front end section of the steering shaft 5 is connected to the rear end section of an intermediate shaft 8 by way of a universal joint 7, and the front end of the intermediate shaft 8 is connected to the input shaft 3 by way of a separate universal joint 9.
A tilt and telescopic type steering apparatus, wherein it is possible to adjust the forward-backward position and the up-down position of the steering wheel 1, is widely used as a steering apparatus. The following kind of construction is employed in order to achieve this kind of tilt and telescopic mechanism. First, the steering shaft 5 is constructed by combining an inner shaft 12 and an outer shaft 13 such that rotation force can be transmitted, and so that relative displacement in the axial direction is possible, and the forward-backward position of the steering wheel 1 can be adjusted by relative displacement in the axial direction between the inner shaft 12 and outer shaft 13.
The steering column 6 is constructed such that the portion on the front end side of an outer column 11 fits around the portion on the rear end side of an inner column 10 such that relative displacement in the axial direction is possible, where the forward-backward position of the steering wheel 1 can be adjusted by this relative displacement in the axial direction. Moreover, of the steering column 6, the inner column 10 that is located on the front side is supported by part of the vehicle body by way of a housing 14, which together with housing a reduction gear and the like of an electric power-steering apparatus, and to which an electric motor 15 that is an auxiliary power source for the electric power-steering apparatus, and a controller 16 for controlling power to the electric motor 15 is supported and fastened. In order to achieve the tilt mechanism, a support cylinder 17 is provided in the left-right direction on the front end of the top section of the housing 14, and a horizontal shaft 18 such as a bolt that is inserted through this support cylinder 17 supports the front end section of the steering column 6 by way of the vehicle body so that the rear section of the steering column 6 can pivotally displace in the up or down direction.
In order to make it possible to adjust the tilt position and the telescopic position of the steering wheel 1, the outer column 11 is supported by a column-side bracket 22 so as to be able to move in the forward-backward direction and up-down direction. In order for this, as illustrated in FIG. 16, a slit 19 is formed in the bottom surface of the front half section of the outer column 11 so that the inner diameter of this front half section of the outer column 11 can elastically expand or contract. Furthermore, a pair of thick plate shaped supported plate sections 21 are provided in the portions on both sides in the width direction of the slit 19. These supported plate sections 21 displace together with the outer column 11 when adjusting the position of the steering wheel 1, and function as a displacement-side bracket.
In a state where the steering wheel 1 is held in the adjusted position, the supported plate sections 21 are firmly held between a pair of left and right support plate sections 24 of the column-side bracket 22. Long holes 25 in the up-down direction that have an arc shape that is centered about the horizontal shaft 18 are formed in the support plate sections 24, and long holes 26 in the forward-backward direction that extend in the axial direction of the outer column 11 are formed in the supported plate sections 21. An adjustment rod 27 is inserted through the long holes 25 in the up-down direction and the long holes 26 in the forward-backward direction. A head section 28 that is formed on the base end section (right end section in FIG. 16) of the adjustment rod 27 engages with one of the long holes 25 in the up-down direction that are formed in one of the support plate sections 24 (right side in FIG. 16) so that rotation is prevented and only displacement along this long holes 25 is possible. On the other hand, a nut 29 is screwed onto the tip end section (left end section in FIG. 16) of the adjustment rod 27. This nut 29 can be rotated and driven by an adjustment lever 33.
When adjusting the position of the steering wheel 1, by rotating the adjustment lever 33 in a specified direction (downward), the nut 29 is rotated and driven, which expands the space between the head section 28 and the nut 29 and releases the force by which the support plate sections 24 hold the supported plate sections 21. At the same time, the inner diameter of the portion on the front section of the outer column 11 into which the rear section of the inner column 10 is fitted is elastically expanded, and the surface pressure that acts on the area of contact between the inner circumferential surface of the front section of the outer column 11 and the outer circumferential surface of the rear section of the inner column 10 is reduced. In this state, it is possible to adjust the up-down position and the forward-backward position of the steering wheel 1 within the range that the adjustment rod 27 is able to displace inside the long holes 25 in the up-down direction and the long holes 26 in the forward-backward direction.
After the steering wheel 1 has been moved to a desired position, by rotating the adjustment lever 33 in the opposite direction (upward) from the specified direction, the space between the head section 28 and the nut 29 contracts, and the support plate sections 24 firmly hold the supported plate sections 21. At the same time, the inner diameter of the portion on the front section of the outer column 11 into which the rear section of the inner column 10 is fitted elastically contracts, causing the surface pressure that acts at the area of contact between the inner circumferential surface of the front end of the outer column 11 and the outer circumferential surface of the rear section of the inner column to increase. In this state, the up-down position and the forward-backward position of the steering wheel 1 is maintained in the adjusted position.
On the other hand, in this kind of steering apparatus for an automobile, in order to protect the driver during a collision accident, construction is necessary that allows the steering wheel 1 to displace in the forward direction while absorbing the impact energy. In other words, during a collision accident, after a primary collision in which an automobile collides with another automobile, a secondary collision occurs in which the body of the driver collides with the steering wheel 1. During this secondary collision, in order to protect the driver by lessening the impact that is applied to the body of the driver, construction is widely employed in which the steering column 6 that supports the steering wheel 1 is supported by the vehicle body so as to be able to break away in the forward direction due to an impact load in the forward direction caused by the secondary collision.
In order for this, as illustrated in FIG. 16, a pair of top plates 43 are provided on the top end sections of the pair of left and right support plate sections 24 of the column-side bracket 22 so as to protrude on the sides of the steering column 6, and locking notches 34 are provided in these top plate sections 43 so as to be open on the edge on rear end of the top plate sections 43. Locking capsules 36 that are fastened to the vehicle body by bolts (not illustrated in the figure) lock in these locking notches 34. In each of the locking capsules 36, engagement grooves 66 for engaging with the edge sections on the left and right sides of the locking notches 34 are formed on surfaces of the left and right side thereof, and a through hole 67 in the up-down direction through which a bolt (not illustrated in the figure) is inserted is formed in the middle sections thereof.
During a collision accident, a large impact load in the forward direction is applied from the driver's body to the steering column 6 by way of the steering wheel 1 and steering shaft 5. This causes a tendency for the steering shaft 5 and steering column 6 to contract along the entire length while absorbing the impact energy. As a result, as the column-side bracket tends to displace in the forward direction together with the outer column 11, the locking capsules 36 remain in position together with the bolts. Consequently, these locking capsules 36 come out toward the rear from the locking notches 34, which allows the steering wheel 1 to displace in the forward direction.
In this kind of conventional construction, the column-side bracket 22 is supported by the vehicle body so as to be able to break away in the forward direction during a secondary collision at two locations on the left and right sides. Therefore, from the aspect of the allowing stable forward displacement of the steering wheel 1 without tilting with respect to the axial direction during a secondary collision, simultaneous disengagement of the pair of left and right locking capsules 36 from the locking notches 34 very important. However, performing tuning in order for simultaneous release of the left and right engaged states requires much time and work because it is affected by resistance such as friction resistance and shear resistance against the release of the engagement of these members, and left and right unbalance in the inertial mass of the portions that displace in the forward direction together with the steering column 6.
In order to stabilize the break away of the steering column in the forward direction during a secondary collision, preferably, as disclosed in JPS 51-121929 (U), the steering column 6 is supported by the vehicle in the center section in the width direction so as to be able to break away. In other words, by using construction wherein the steering column 6 is supported at the center section in the width direction as disclosed in JPS 51-121929 (U) instead of using construction wherein the steering column 6 is supported at two locations in the width direction as illustrated in FIG. 16, it becomes difficult for the steering column 6 to tilt when breaking away in the forward direction, and thus it becomes easier to perform tuning in order to protect the driver. Therefore, even in the conventional construction illustrated in FIG. 16, it is necessary to devise construction that supports the steering column 6 in the center section in the width direction, however, that does not mean that the construction disclosed in JPS 51-121929 (U) can be applied right away as it is.
In the conventional construction illustrated in FIG. 16, as a secondary collision proceeds, there is a possibility that the locking capsules 36 will come all the way out from the locking grooves 34. In that case, support of the outer column 11 by the column-side bracket 22 is lost, and there is a possibility that the steering wheel 1 will drop excessively. In such a situation, operation of the steering wheel 1 becomes difficult.